Method of preferentially heat treating steel articles



i June 22, 1954 METHOD OF PREFERENTIALLY HEAT TREATING STEEL ARTICLESOriginal Filed April 28, 1948 2 Sheets-Sheet 1 fig INVENTOR.

ROBERT J3 Ll/V/VEY R. J. LINN EY 2,681,874

' 2 Sheets-Sheet 2 June 22, 1954 METHOD OF PREFERENTIALLY HEAT TREATINGSTEEL ARTICLES Original Filed April 28, 1948 VENTOR. Z/NNEY IN IEOBEIE'TJ BY RIC HEY, WA rrs, Ease-Prom? MCNFN/V) Patented June 22, 1954 UNITEDSTATES ATENT OFFICE METHOD F PREFERENTIALLY HEAT TREATING STEEL ARTICLES23,693. Divided and this application October 23, 1951, Serial No.252,629

6 Claims. 1

This invention relates generally to the art of metal heat treatment, andparticularly to an improved method of the tempering of ferrous metalobjects, especially drill bits.

In the manufacture of certain metal articles: it is quite important thatthey should be properly tempered, that is, so cooled from aheat-treating temperature that they will possess the desired properties.For example, steel bits used with drilling machines for drilling holesin hard rock should be properly and uniformly tempered. Frequently aplurality of bits of progressively decreasing size are used in drillinga single hole, the largest drill being used first and the smaller onesfollowing thereafter in the decreasing order of their sizes. If one ofthe bits should be improperly tempered, for example, if it should besofter than the succeeding bits, it will not make a hole of the desiredsize for succeeding bits and may stick in the hole. Hence, it isimportant that each bit of a set of drill bits should be properly anduniformly tempered, but it is also important that all bits whetherintended for use in a certain set or not should be properly anduniformly tempered.

So far as I know, it was not possible, prior to the present invention,automatically to temper steel drill bits properly and uniformly or toinsure that the tempering will be proper and uniform from bit to bit. Bythe present invention I am able not only to temper steel drill bits andalso other metal objects properly, but also to insure that all theobjects of the same composition will be tempered properly andsubstantially Llll'iformly.

The present invention is predicated on the discovery that proper anduniform tempering may be attained by cooling highly heated metal objectswith a predetermined amount of cooling liquid maintained atsubstantially constant temperature, or by exposing the highly heated objects to the cooling effect of a substantially uniform temperaturecoolant for a predetermined length of time, then transferring the thuspartially cooled objects, without substantial decrease in theirtemperature, to a second cooling liquid maintained at a lowertemperature and allowing the objects to cool to the temperature of thatliquid.

In the drawings accompanying and forming a part of this specification,

Fig. l is a top plan view of one form of apparatus embodying the presentapparatus invention and with which the present method invention may bepracticed;

Fig. 2 is an elevational view taken from the chute side of. theapparatus of Fig. 1; and

Fig. 3 is an elevational view taken from the left side of Fig. 1.

In the drawings the reservoir I is provided with a drain pipe 2controlled by a valve 3 and an overflow pipe l. Liquid is maintained inreservoir I to the level indicated by line 5. Liquid may be brought intoreservoir I through pipe 5 which is equipped with a thermostaticallycontrolled valve "I. In this case the thermostat 8 is of the electricaltype and is connected through lead ii, panel I!) and lead II to anelectrical device I2. The thermostat 8 and the device I2 may be,respectively, the well-known Mercoid thermostat control and Mercoilmagnetic valve. When the temperature of the liquid in reservoir I risesabove a predetermined point the thermostat 3 actuates the valve I2 andopens valve I, thereby admitting cold liquid through pipe 6. Since thedischarge end of pipe 6 is remote from the thermostat 8, the incomingfluid will continue to flow for some little time before the thermostat 8will be actuated by a lowering of the temperature of the liquid inreservoir I to ole-energize the valve control device and close the valve1 against further entry of cold liquid.

Adjacent to the thermostat 8 is disposed a pump I3 which communicateswith the interior of the reservoir I and serves to withdraw liquidtherefrom and to force it through pipe I l and into the top of a hollowshaft presently to be described. The pump I3 is actuated by a motor I5.

Two upright beams I 6 are disposed on opposite sides of reservoir I andare connected together at their upper ends by a channel I"? and at apoint some little distance above the top of reservoir I by a pair ofchannels I8. An upright leg or beam I9 also located outside of reservoirI is connected at its upper end to one or more channels 20 which extendhorizontally toward and connect to one of the channels I8. A plate orplatform 25 rests on channels 2!] and is secured to channels [8 and 2tand serves as a support for a power unit consisting of a motor 23 and areduction gearing device 23. Panel It, above mentioned, is secured tochannel II, to one of the uprights Iii and, to plate 2I.

The plate 2 I supports a thrust bearing 25 which, in turn, rotatablysupports the hollow shaft 28 above mentioned. This shaft passes througha pillow block or bearing 21 on channel IT. A sprocket 28 is keyed toshaft 2% and is connected to the reduction gearing device 23 by adriving of tank 30, and an enlarged upper end 33 proi vided with ascreen on which an object to be tempered may be placed. It will beunderstood that when pump 13 withdraws liquid from l and forces itthrough pipe I4 into hollow shaft 25, such liquid will fill the tank andwill flow out through pipes 32 and up through the perforations in thescreen and against an object on the screen. It will also be understoodthat when the motor 22 is actuated the chain 29 will rotate shaft 25,tank 30 and members 3! and that by varying the speed of rotation of theshaft objects on those members may be subjected for various lengths oftime to cooling liquid flowing thereagainst through said members.

A magnet is mounted on supports ii which are connected to reservoir I byarms 52. This magnet is adjustably positioned relative to metallicarticles on the spray-heads, so that vhen en-- ergized the magnet mayattract to itself and thereby remove from an adjacent spray-head amagnetic metal article on the latter. The magnet 40 is alternatelyenergized for a short period of time and then is de-energized foranother short period of time. The top of tank 30 is provided with aplurality of pegs 15 positioned radially inward of the respectivespray-heads 3i. These pegs are so disposed as to make contact with theswitch closing member :lfi of a limit switch il which is connected to asuitable source of electric current and also to the windings of magnet4|]. When one of these pegs 45 closes the contacts of the limit switch4? the electrical current energizes magnet 49 and the magnet in turnattracts to itself a metal object on the spray-head adjacent the magnet.When the peg 65 moves on and permits the contacts of the limit switch41' to separate, the current to magnet it is interrupted and the metalobject which had been attracted to the magnet is allowed to fall. Hithis way the magnet is energized for a short time and then isde-energized for another short time, and the energization occurs when aspray-head is adjacent to the magnet.

An inclined chute 59 is disposed with its upper end in position toreceive metal articles which r fall from the de-energized magnet 40. Thelower end of this chute 50 is disposed above a stationary tank 5| sothat metal articles dropping from magnet 40 may slide into that tank. Anopentop screen-basket 52 is provided in tank 5! to receive sucharticles. This tank also contains a cooling liquid which may bemaintained at above a predetermined temperature by means of a heat ingunit 53 which may be of any suitable construction, for example, thewell-known Calrod immersion heating unit.

The general operation of the above described apparatus will beunderstood from the foregoing description. However, when it is to beoperated to temper steel drill bits for hard rock drilling it may beoperated substantially as follows: The motor [5 is energized and pump I3circulates coolant from reservoir I through pipe [4, shaft 26, tank 30and spray-heads 3! and brings the level of coolant in tank 30 to abovethe tops 4 of heads 3| so that the coolant will overflow the heads andreturn to reservoir I. The motor 22 is energized and tank 30 is rotated.Then steel drill bits which have been heated to the proper temperature,which may be about 1440 F. for one particular kind of steel, are removedfrom the heating furnace and are placed one at a time points down on thespray-heads when they reach the position indicated by the letter X inFig. l and while tank 30 is rotating. As tank 30 rotates, the pressureexerted on the cooling liquid is so regulated that the liquid bubbles upthrough the spray-heads and to a predetermined distance thereabove whichis sufiicient to cover only the 1- drilling points of the bits or aboutfor the average size jack bit. This liquid is maintained at atemperature under 75 F. preferably at about 72 F. The liquid thusregulated as to pressure and temperature cools the points from the timethey leave point X until they reach the position indicated by the letterY in Fig. 1. When a bit reaches that position, a peg 45 several stationsbehind that spray-head will close the circuit through limit switch 41,thereby energizing magnet 40. When energized this magnet attracts toitself the drill bit on the spray-head at station Y and whende-energized drops that drill bit onto chute 50 and the bit slides intotank 5|.

It will be understood that during the time of about 53 seconds whichelapses between the placing of a bit on a spray-head at station X andthe time the drill bit is removed therefrom at station Y, the liquidcoming into contact with the drill bit will have lowered the temperatureof the drill bit considerably, for example, from about 1440 F. to about900 F., that the bit will then be at a temperature within the magnetictemperature range of the steel, and that the temperature of the drillbit will not sensibly decrease between the time it is removed at stationY and the time it arrives in tank 5!. The speed of r0- tation of tank 30should be so adjusted for bits of different sizes that the bits arecooled through the just mentioned range during one revolution of thetank. Higher or lower speeds may, of course, be used when smaller orgreater decreases in temperature are desired.

Drill bits of the type referred to herein are composed of steel whichcan be made quite hard by treatment. While drill bits are made fromsteels of different S. A. E. numbers, the compositions which aresuitable contain between about 370% and 86% of carbon, between about 40%and of manganese, about 133% maxi mum of sulfur and of phosphorous, withthe remainder being iron containing small amounts of other impuritiesbut without any substantial amounts of alloying elements. The cuttingedges are often formed on these bits when the carbides in the steel arein a spherodized condition and the steel is soft and machinable as aresult thereof. Then the steel is heated to such a temperature as willresult in a complete solution of the carbides which in this case isabout ll40 F. Then the dissolved carbides in the cutting edge portionsare precipitated as very fine grain martensite more or less uniformlythroughout those portions by quenching the cutting edges of the bit withresultant hardening of those portions. This quenching step is carriedout by quickly lowering the temperature of the cutting edge portionsfrom about 1440" F. to about 900 F. in a short space of time as bybubbling water at about 72 F. to about 75 F. over the cutting surfacesfor about 51 seconds on the average.

The entire bit is cooled by the extraction of heat from the body of thebit through the surfaces in contact with the water but the cooling rateof the metal beyond the cutting edge portions is less rapid and hencethe body part of the bit is more ductile and resistant to breakage thanthe cutting edges. The thus quickly cooled article is transferred,preferably magnetically, when at a temperature of about 900 F. into abody of water maintained, for example, at about 192 F. where it isallowed to cool for about minutes. If desired, the bit may be reheatedto a drawing temperature to reduce the brittleness of the cutting edgeportions.

Since the cooling rate of the drill bits in tank 5| should not be toorapid, the temperature of the liquid is maintained above a predeterminedminimum temperature by the heating unit 53.

Various cooling liquids may be used in reservoir l and stationary tank5|, as desired. Water may be used in reservoir l but its temperatureshould not be permitted to rise beyond a certain point for if it becomestoo highly heated, due to heat extracted from the bits, it will not coolthe bits below their non-magnetic range and hence the magnet 40 will notattract them to it. When the liquid in reservoir I is maintained at atemperature not in excess of about 75 F. and the speed of rotation oftank and the rate of liquid flow through the spray-heads are properlyadjusted, tool bits having a temperature of about 1440" F. when placedon the spray-heads will be cooled to below their non-magnetictemperature range before they reach the magnet and hence will beattracted to the magnet and removed from the spray-heads. By suitablysetting the thermostat 8 the temperature of the coolant in reservoir maybe maintained substantially constant, as above mentioned.

The coolant preferred in tank 5| is Water and its temperature ispreferably maintained close to its boiling point by the heating unit inthe bottom of the tank, 192 F. having been found to be satisfactory.

Each bit cools to about the temperature of the water in tank 5| withinabout 10 minutes and may then be removed for subsequent treatment.

While the foregoing detailed description is specific to the tempering ofdrill bits, it will be understood that other articles may be temperedthrough the use of the above-described apparatus in accordance with themethod of this invention, and that by adjusting the speed of rotation oftank 30 and the temperature of the coolant in reservoir 1 and the rateor amount of coolant flow through spray-head 3|, various metal objectsmay be cooled throughout various temperature ranges and to varioustemperatures, depending on the characteristics desired in the objectsand obtainable by such variations in the time, rate and nature of thetempering action. It will be understood that by varying the kind andtemperature of the coolant in tank 5|, the rate of cooling of metalarticles therein may be varied with some variation in the properties ofthe articles cooled under those conditions.

This application is a division of my application Serial No. 23,693,filed April 28, 1948, now Patent No. 2,596,493 which was acontinuationin-part of my application Serial No. 499,398, now abandoned.

Having thus described the present invention so that others skilled inthe art may be able to understand and practice the same, I state that 6.what I desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. The method of heat treating and preferentially hardening surfaces andmaking ductile the remainder of steel articles containing between about.70% and about of carbon, between about 40% and about .60% of manganese,less than about .03 of phosphorus and of sulphur, the remainder beingiron with the usual amounts of other impurities which comprise the stepsof exposing to the atmosphere such an article which is at a temperatureof about 1440 F. and has its carbides in solution, flowing water at atemperature of about 75 F. against part of the surface of said articleand thereby quenching such surface, precipitating the carbides thereinas finegrained martensite and hardening said surface, and thereuponcompleting the cooling in water near its boiling temperature.

2. The method of heat treating and preferentially hardening surfaces andmaking ductile the remainder of steel articles containing between about.'70% and about .90% of carbon, between about .40% and about .60% ofmanganese, less than about 03% of phosphorus and of sulphur, theremainder being iron with the usual amounts of other impurities, whichcomprise the steps of exposing to the atmosphere such an article whichis at a temperature of about 1440 F. and has its carbides in solution,flowing water at a temperature of about 75 F. against surfaces at oneend of said article and thereby quenching said surfaces, precipitatingthe carbides therein as finegrained martensite, hardening said surfaces,and reducing the temperature of the article to about 900 F., thenimmediately transferring said article magnetically to a bath of water ata temperature of about 192 F. and removing the article from said bathafter it has been cooled to the bath temperature.

3. The method of heat treating and preferentially hardening surfaces andmaking ductile the remainder of steel articles containing between about370% and about .90% of carbon, between about .40% and about .60% ofmanganese, less than about 03% of phosphorus and of sulphur, theremainder being iron with the usual amounts of other impurities whichcomprise the steps of exposing to the atmosphere such an article whichis at a temperature of about 1440 F. and has its carbides in solution,flowing water at a temperature of about 75 F. against surfaces at oneend of said article until the article has been cooled to about 900 F.,thereupon transferring the article magnetically into a bath of water ata temperature near its boiling temperature, and cooling the article insaid 'bath to about the temperature of the water.

4. A method of heat treating and preferentially hardening the cuttingsurfaces and making ductile the shanks of high carbon steel drill bitswhich comprises the steps of heating the bit at a temperature of about1440 F. until the carbides therein have dissolved, exposing the thusheated article to the atmosphere, quenching and cooling the drillsurfaces of the bit from a temperature of about 1440 F. to about 900 F.by flowing water at a temperature of about 75 F. against said surfaceswhile the remainder of the article is exposed to the atmosphere and iscooled at a lower rate, and then cooling the entire article to about 192F. by immersing it in water at about that temperature.

5. A method of heat treating and preferentially hardening the cuttingsurfaces and making ductile the shanks of high carbon steel drill bitswhich comprises the steps of heating the bit at a temperature of about1440 F. until the carbides therein have dissolved, exposing the thusheated article to the air While flowing water at a temperature of about75 F. against the drill surfaces of the bit and cooling said surfaces toabout 900 F., While the remainder of the article is exposed to the airand is cooled at a slower rate, thereupon transferring the bitmagnetically to a bath of water maintained near its boiling temperatureand cooling the entire bit in the bath to about the water temperature.

6. The method of heat treating and preferentially hardening the cuttingsurfaces and making ductile the shanks of steel drill bits containingbetween about .70% and about .90% carbon, between about .40% and about.60% of manganese, less than about .03% of phosphorus and of sulphur,and the remainder being iron with the usual amounts of other impurities,which comprises the steps of heat treating the bit at a temperature ofabout 1440 F. until the carbides therein have dissolved, exposing thethus heated article to References Cited in the file Of this patentUNITED STATES PATENTS Number Name Date 2,441,628 Grifiiths et al May 18,1948 FOREIGN PATENTS Number Country Date 580,728 Great Britain Sept. 18,1946 OTHER REFERENCES High Speed Steel, by Grossman & Bain, page 68,1931.

Tool Steels, by Gill et al., pages 219 and 220, 1944.

1. THE METHOD OF HEAT TREATING AND PREFERENTIALLY HARDENING SURFACES ANDMAKING DUCTILE THE REMAINDER OF STEEL ARTICLES CONTAINING BETWEEN ABOUT.70% AND ABOUT .90% OF CARBON, BETWEEN ABOUT .40% AND ABOUT .60% OFMANGANESE, LESS THAN ABOUT .03% OF PHOSPHORUS AND OF SULPHUR, THEREMAINDER BEING IRON WITH THE USUAL AMOUNTS OF OTHER IMPURITIES WHICHCOMPRISE THE STEPS OF EXPOSING TO THE ATMOSPHERE SUCH AN ARTICLE WHICHIS AT A TEMPERATURE OF ABOUT 1440* F. AND HAS ITS CARBIDES IN SOLUTION,FLOWING WATER AT A TEMPERATURE OF ABOUT 75* F. AGAINST PART OF THESURFACE OF SAID ARTICLE AND THEREBY QUENCHING SUCH SURFACE,PRECIPITATING THE CARBIDES THEREIN AS FINEGRAINED MARTENSITE ANDHARDENING SAID SURFACE, AND THEREUPON COMPLETING THE COOLING IN WATERNEAR ITS BOILING TEMPERATURE.